My computer is as silent as I could make it. Unfortunately, the hard drive was noisy. It is not noisy in the sense that you can hear the drive read/writes, but it was squealing when the computer is turned on til the computer is turned off.
Using several hard drives, I can tell when the noise level is too much. Furthermore, it was a backup hard drive that did nothing.
Therefore, I took it out and did some testing because I thought that the problem was not the drive, but the way I screwed it into the case.
I have a IDE or SATA drive to USB cable with a power cord that costs me about $20. This allows me to connect the hard drive to a computer externally. You can see the cable at http://www.tigerdirect.ca/applications/SearchTools/item-details.asp?EdpNo=3249952&CatId=470
I put the hard drive on the table and turned on the power.
To make a long story short, it is in my computer spare parts storage bin with a label that reads noisy.
This forum may help you when you decide to buy a replacement hard drive.